M308 B-Value for Semitec 104GT-2 104NT-4-R025H42G

[xadox]

In the past I was using cheap China NTC thermistors for the Hotend.
Now I want to try a Semitec 104GT-2 104NT-4-R025H42G.

How do I calculate the right B-Value.

At the moment I have this config:

; Heaters
M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0                          ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B0 S1.00                               ; disable bang-bang mode for the bed heater and set PWM limit
M140 H0                                        ; map heated bed to heater 0
M143 H0 S120                                   ; set temperature limit for heater 0 to 120C
M143 H1 S290
M308 S1 P"e0temp" Y"thermistor" T100000 B4138  ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1                           ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S1.00                               ; disable bang-bang mode for heater  and set PWM limit

I am using a Duet 2 with the lastest v3 firmware.

[Veti]

in the configurator when you click on the beta value a popup comes up that lets you select the semitec
https://configtool.reprapfirmware.org/Heaters

its B4725 C7.06e-8

[xadox]

Ahhh... I didn't know that I can select the thermistor there too. I thought I could only enter the value there.

Thanks a lot.

[xadox]

I switched the Thermistor. Changed the values in config.g into the following:

M308 S1 P"e0temp" Y"thermistor" T100000 B4725 C7.06e-8 ; Semtec Thermistor
; M308 S1 P"e0temp" Y"thermistor" T100000 B4138  ; configure sensor 1 as thermistor on pin e0temp

Re-Tuned the Hotend.
But now I get worse results in print than before:

Left Semitec | Right Cheap China NTC

[Veti]

@xadox said in M308 B-Value for Semitec 104GT-2 104NT-4-R025H42G:

B4138

you were most likely printing at the wrong temperature with you chinese thermistor.

what temperature are you printing with what material?

[xadox]

@Veti Both were printed with M4P PETG@245C

[Veti]

try printing at 225

[xadox]

@Veti I think the Config-Generator seems to have a small bug.
Since the Semitec should have around 100KOhm at 25°C (Datasheet):

But the Config-Generator creates it with 100000:

I measured the resistance at 25°C and it is about 100KOhm.

[Veti]

i am not sure i follow 100K = 100000

[xadox]

@Veti You are of course absolutely right.
I forgot that the data is in Ohm.

[xadox]

Ok. I will try printing now with lower temp @225C.

[xadox]

@Veti You are a genius:
Printed @225C

[Veti]

so this tell you that the temperature with you china thermistor was off by about 20 degrees